I was recently lucky enough to witness an extraordinary fault on a beautifully maintained MTO Sport. The aircraft lined up to depart the field and started to prerotate, as so many of us are aware this is often the point at which we realise we are not going home yet. On investigation by a qualified engineer and through a process of elimination, it was discovered that that airline that feeds the belt tension cylinder appeared to be blocked. On further examination the engineer established that where the tube was cable tied around under the gearbox that the two (corners) that it went around had clearly got flattened. It would seem as though the tube when it gets hot was softening and then when cooling was remembering its flat state rather than returning to its round state, thus reducing the airflow to the cylinder and preventing the pulley from becoming tensioned enough. Simple fix too but incredibly difficult to track the fault. There is one to rule out when having prerotator issues.
Having seen this I thought I would check mine, it would seem that after 1000 hours mine was actual fine, when undoing all the cable ties though and freeing up both the tubing and the wires, I found that my sensor cable was quite badly chafed and needed protecting before clipping back.